They're pretty secretive about what they use, but they describe it as fruity, attenuative and London-style. All of these are relative terms, and can be easily manipulated by temp and pitch rate, of course. There's a pretty good chance their house strain isn't commercially available on the homebrew scale. WLP006 and WLP007/WY1098 more or less fit the descriptions, although I'm sure other strains do as well.